Renal dose adjustment: what changes and why
An estimated 37 million American adults have CKD, according to the CDC. Most of them are on multiple medications. And a significant proportion of those medications are eliminated through kidneys that aren't working at full capacity.
Why renal function changes drug levels
The kidney filters drug out of the blood at a rate determined by its own condition. Reduce kidney function by half and renally-cleared drugs accumulate at roughly twice the rate. Keep the same dose and interval in a CrCl 30 patient as you'd use in a CrCl 90 patient, and you're building toward toxicity. The solution is either a lower dose, a longer interval between doses, or both.
CrCl vs eGFR: which one to use for dosing
Most drug dosing references were developed using the Cockcroft-Gault equation, which calculates creatinine clearance (CrCl) using age, weight, sex and serum creatinine. Modern labs report eGFR using the CKD-EPI formula instead. Most current drug labels and dosing tables still specify Cockcroft-Gault, but the National Kidney Foundation now recommends moving medication-related decisions toward race-agnostic eGFR, and the FDA's 2024 guidance for industry points the same direction for new drugs. Until a specific label or protocol says otherwise, use our Creatinine Clearance Calculator to get the value most existing references still expect.
Drugs that are especially dangerous in renal impairment
Metformin: contraindicated below CrCl 30 due to lactic acidosis risk. NSAIDs: worsen renal function and should be avoided in CKD. Nitrofurantoin: doesn't reach adequate urinary concentrations below CrCl 45 and increases toxicity risk. Gentamicin and vancomycin: narrow therapeutic index antibiotics requiring level monitoring and extended intervals in renal impairment. Methotrexate: toxic accumulation in renal failure. Lithium: renally cleared with narrow therapeutic index; requires frequent monitoring in CKD. Always check interactions alongside renal adjustments using our Drug Interaction Checker.
Dialysis patients
Haemodialysis removes some drugs efficiently; others are poorly dialysed. The dose timing relative to dialysis sessions matters, and NIDDK's overview of hemodialysis is a useful primer on the standard 3-times-weekly, roughly 4-hour session schedule that dosing intervals are often built around. Patients on dialysis need specialist renal pharmacy review. This tool provides general guidance only and should not be used as the sole reference for dialysis patients.